docs: def get_idxs(data, eid2idx):
      """
      Convert from event IDs to event indices.
  
      :param data: an array with a field eid
      :param eid2idx: a dictionary eid -> idx
      :returns: the array of event indices
      """
      uniq, inv = numpy.unique(data['eid'], return_inverse=True)
      idxs = numpy.array([eid2idx[eid] for eid in uniq])[inv]
      return idxs